High voltage rectifier



Jam 29, 1935. D. v. EDWARDS ET AL 1,989,132

HIGH VOLTAGE RECTIFIER INVENTORU Filed Jan. 14, 1931 Patented Jan. 29, 1935 V HIGH VOLTAGE 7 Donald v. Edwards, New York, a. Y., Ma Earl K.

Smith, East Orange, N. J., assignors to Electrons, Inc., of Delaware, a corporation of Delaware Application January 14, 1931, Serial No. 508,686

Claims.

5 whereby the tube may be operated at high plate voltage.

The invention will be described with reference to the accompanying drawing, in which Fig. 1 illustrates a discharge tube embodying the invention, and

Fig. 2 illustrates a modified form.

In the drawing 1 represents the tube which is filled with gas at suitable pressure. Preferably we employ argon, usually at about one-half millimeter of mercury pressure, although mercury or other gas or mixtures thereof may be employed to provide an ionizable medium. 2 is the plate; 3 the grid; 4 the filament and 5 the cathode, pref erably in the form of an open ended can. In the form shown in Fig. 1 the plate or anode is made of tantalum, while that of Fig. 2 is of carbon. A shield 6 encloses the plate 2, being preferably supported by one or more supports 7 clamped to the reentrant portion or stem of the tube, and having an opening 8 in the front face thereof, the opening being covered by a screen 9 of suitable mesh. The control electrode or grid 3 also has a central opening 10 covered by a screen 11 of suitable mesh. In the form shown in Fig. 1 the grid is supported by one or more supports 12 clamped to the reentrant part of the tube opposite to that supporting the plate shield 6, whereas in Fig. 2 the supports 12 are clamped to the same reentrant part as are the supports for the plate shield. The cathode 5 is preferably oxide coated and may be direct heated, as by applying the coating to the filament 4, or indirectly heated. The oxide coating may also be applied to the inside of the can 5 if desired.

The shield 6 should, preferably, completely surround the plate and should be maintained at a voltage less than the breakdown voltage of the tube. A convenient way to do this is to connect it electrically to the cathode by conductors 13 and 14, or to the grid by suitable conductors 13 and 15, or to a low voltage transformer tap through a resistance. Furthermore, the shield should be spaced from the plate to take advantage of the mean free path principle, 1. e. that if two conductors are spaced apart less than the mean free path of the atoms and a very large potential is applied to one conductor, the atoms will be split up but due to the scarcity of atoms in the path of the resulting ions and electrons no other collisions occur and no further ionization starts, with the result that only a very small current clears the space between the two conductors of atoms which could conduct electricity. In practice we have found that this space becomes well cleared even if the spaces are from ten to fifty times that of the mean free path.

The size of the opening 8 will be regulated to neutralize some of the electrostatic lines of force from the plate and yet allow enough to get through to give the same effect on the grid and cathode as a plate of a voltage lower than the gas breakdown voltage. The spacing between the wires of the screen 9 and the diameter of the wires may be varied in regulating the opening.

Thus, although applying a, high potential to the plate, the net electrostatic result in the whole tube is the same as if a very much lower plate potential were used, thus obviating danger of breakdown from grid to plate or from filament to plate, or plate to grid in the reverse cycle.

It will be understood that the arrangement and design of the several mechanical parts may be modified without departing from the spirit of the invention. For example, a part of the grid structure may be brought close enough to the plate to perform the shielding function and the screen portion properly positioned to perform the grid control function; and the distance between shield and plate will be measured functionally, i. e. sufiiciently close to prevent discharge in view of the mean free path of the particular gas employed at the pressure employed.

We claim:

1. In a rectifier of the gaseous type, an anode, a cathode, a control grid, and a shield located a distance from the anode comparable to the mean free path of the gas, said control grid being located remote from the anode compared to said distance, and means for maintaining the said grid and shield at substantially the same potential.

2. A rectifier tube comprising an ionizable medium, an anode, a cathode, a control electrode, and a conductive member interposed between the anode and the control electrode and spaced from the anode a distance determined by the mean free path in said medium whereby ionization of that portion of the medium between said member and anode is prevented, said member having an impervious portion and a discharge opening which is substantially smaller in area than the discharge face of said anode.

3. In a rectifier of the gaseous type, an anode, a cathode, a grid, and a shield interposed between the anode and the grid and spaced from the anode a distance comparable to the mean free path of the gas, the spacing between the grid and shield being large relative to the mean free path and said shield having means for reducing the percentage of positive anode field which reaches the grid.

4. In a rectifier of the gaseous type, an anode, a cathode, a grid, and a shield interposed between the anode and the grid, said shield being spaced from the anode a distance comparable to the mean free pathot the gas and having a restricted opening which controls the percentage of the positive anode field which reaches the grid, said grid being spaced from the shield opening a large distance compared to the mean free path distance. I

5. In a rectifier of the gaseous type, an anode, a cathode, a starting control grid, an ionizable medium, and a shield having a portion thereof disposed in the space between the anode and grid, said space being sufllciently large relative to the pressure of said medium for general ionization by collision, and said shield being so spaced relative to the anode and grid respectively "that the breakdown voltage in said medium from shield to grid to shield.

EARL K. SMITH. DONALD V. EDWARDS. 

